linux-kernel - Re: [PATCH v7 2/3] I2C: mediatek: Add driver for MediaTek I2C controller

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Message-ID: <1431928701.22349.22.camel@mtksdaap41>
Date:	Mon, 18 May 2015 13:58:21 +0800
From:	Eddie Huang <eddie.huang@...iatek.com>
To:	<wsa@...-dreams.de>
CC:	Sascha Hauer <kernel@...gutronix.de>,
	<srv_heupstream@...iatek.com>, "Rob Herring" <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Xudong Chen <xudong.chen@...iatek.com>,
	"Liguo Zhang" <liguo.zhang@...iatek.com>,
	<linux-i2c@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v7 2/3] I2C: mediatek: Add driver for MediaTek I2C
 controller

Hi Wolfram,

Narrow down CC-list.
Please see my reply below.

On Tue, 2015-05-12 at 14:58 +0200, wsa@...-dreams.de wrote:
> > +#include <linux/kernel.h>
> > +#include <linux/module.h>
> > +#include <linux/slab.h>
> > +#include <linux/i2c.h>
> > +#include <linux/init.h>
> > +#include <linux/interrupt.h>
> > +#include <linux/sched.h>
> > +#include <linux/delay.h>
> > +#include <linux/errno.h>
> > +#include <linux/err.h>
> > +#include <linux/device.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/mm.h>
> > +#include <linux/dma-mapping.h>
> > +#include <linux/scatterlist.h>
> > +#include <linux/io.h>
> > +#include <linux/of_address.h>
> > +#include <linux/of_irq.h>
> > +#include <linux/clk.h>
> > +#include <linux/completion.h>
> 
> Please sort the includes to avoid duplicates.
OK, will fix it.

> 
> > +struct mtk_i2c_compatible {
> > +	const struct i2c_adapter_quirks *quirks;
> > +	unsigned char pmic_i2c;
> > +	unsigned char dcm;
> > +};
> 
> I wonder if the unsigned char options can be bits in a flags variable?

OK, will fix it.

> 
> > +static const struct i2c_adapter_quirks mt6577_i2c_quirks = {
> > +	.flags = I2C_AQ_COMB_WRITE_THEN_READ,
> > +	.max_num_msgs = MAX_MSG_NUM_MT6577,
> > +	.max_write_len = MAX_DMA_TRANS_SIZE_MT6577,
> > +	.max_read_len = MAX_DMA_TRANS_SIZE_MT6577,
> > +	.max_comb_1st_msg_len = MAX_DMA_TRANS_SIZE_MT6577,
> > +	.max_comb_2nd_msg_len = MAX_WRRD_TRANS_SIZE_MT6577,
> > +};
> 
> I would think plain numbers are much more readable than defines here.
> They are used only once, too.
> 
OK, will fix it.

> > +static const struct of_device_id mtk_i2c_of_match[] = {
> > +	{ .compatible = "mediatek,mt6577-i2c", .data = (void *)&mt6577_compat },
> > +	{ .compatible = "mediatek,mt6589-i2c", .data = (void *)&mt6589_compat },
> > +	{}
> > +};
> > +MODULE_DEVICE_TABLE(of, mtk_i2c_of_match);
> 
> No need for casts.
> 
OK, will fix it.

> > +static inline void mtk_i2c_writew(u16 value, struct mtk_i2c *i2c, u8 offset)
> > +{
> > +	writew(value, i2c->base + offset);
> > +}
> > +
> > +static inline u16 mtk_i2c_readw(struct mtk_i2c *i2c, u8 offset)
> > +{
> > +	return readw(i2c->base + offset);
> > +}
> 
> I am not a big fan of such extremly thin wrappers, but if you like them...
> 
OK, will fix it.

> > +		rpaddr = dma_map_single(i2c->adap.dev.parent, msgs->buf,
> > +						msgs->len, DMA_FROM_DEVICE);
> 
> I think you shouldn't use the adapter device here and later, but the dma
> channel device.
> 
In MTK SoC, each I2C controller has its own DMA, and this DMA can't be
used by other hardware.
So I tend to use DMA directly, not through DMA channel.
Even so, "i2c->adap.dev.parent" is not suitable here. I will change to
use i2c->dev here. (Reference i2c-at91.c).

> > +	/* flush before sending start */
> > +	mb();
> > +	mtk_i2c_writel_dma(I2C_DMA_START_EN, i2c, OFFSET_EN);
> 
> Is mb() really needed when you use writel after that?
> 
mb() should be removed here.

> > +	if (i2c->irq_stat & (I2C_HS_NACKERR | I2C_ACKERR)) {
> > +		dev_dbg(i2c->dev, "addr: %x, transfer ACK error\n", msgs->addr);
> > +		mtk_i2c_init_hw(i2c);
> > +		return -EREMOTEIO;
> 
> -ENXIO. Please check Documentation/i2c/fault-codes for a reference and
> check all your error values.
> 
OK, I will check return values.

> > +	ret = of_property_read_u32(np, "clock-div", clk_src_div);
> > +	if (ret < 0)
> > +		return ret;
> 
> Do we need a property for that in the i2c-block? Can't the clock
> provider driver deliver a properly divided clock already?
> 
Actually, the clock divider implement in I2C controller self.
Clock provider don't have such knowledge to know the divider. The
divider may not be the same in different chip, this is why we put
"clock-div" in device tree. 

> 
> And cppcheck says:
> 
> drivers/i2c/busses/i2c-mt65xx.c:133: style: struct or union member 'mtk_i2c_data::clk_frequency' is never used.
> drivers/i2c/busses/i2c-mt65xx.c:135: style: struct or union member 'mtk_i2c_data::clk_src_div' is never used.
> 
OK, I will remove them.

Thanks your review.
Eddie




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